Like the other oil seeds, soybean consists of the parts of a cotyledon (ca.90%), a germ (ca.2%) and a hull (ca.8%). The soybean is used as material for soybean oil, after its hull is removed but the cotyledon and the germ that are rich in oil are not separated with each other.
When the oil is produced from the soybean, foreign substances such as stem, sheath and other seeds are first removed from a starting soybean material in a selection step for improving quality of a final oil product and defatted cake. Then, the material is provided with elasticity by being subjected to, for example, a heating treatment, crushed by means of a crushing roller or rubber roller and separated into the hull, cotyledon and germ parts. The hull, which contains components such as a pigment that will adversely affect the quality of oil, is removed by means of a vibrating sieve or a sorting apparatus with air. The cotyledon and germ are flaked altogether to destruct their structures and to ease extraction of oil, followed by the extraction with n-hexane to give a crude oil, which is finally purified to yield the soybean oil.
Japanese Patent Laid-Open Application Sho. 59 (1984)-82063 and Japanese Patent Laid-Open Application Hei. 11 (1999)-196803 disclose a method for obtaining the germ part from half-cut soybeans by means of a sieve or sorting with air. In the method the germ part may be separated at a high concentration without suffering any damage. However, it is impossible to treat a large amount of the half-cut soybeans in just one crushing step. Further, a collecting rate of the germ attached to the hull is very low, increasing a load of a flaking machine. For these reasons, it is difficult to extract oil from the germ-enriched part obtained from the half-cut soybeans in view of processing capacity and performance management.
Japanese Patent Publication Sho. 56 (1981)-39176 discloses a method for the concentration of soybean germ by sorting crudely crushed soybeans with air and separating a fraction of 14-60 mesh by means of a sieve. However, since the method will seriously hurt the germ part, the crudely crushed soybeans have to be immediately subjected to the next step. And, the size of the separated soybean fraction is so fine that an amount of the extracted oil will be small, increasing a load in a step for removing a solvent from meal.
Japanese Patent Laid-Open Application Sho. 62(1987)-100256 discloses a method comprising treating crudely crushed soybeans at a high temperature and a high pressure for a certain period of time, releasing them under a low pressure to expand only the germ part, followed by separation of the germ and cotyledon by making use of the difference in their specific gravity. However, it is very dangerous to perform this method at the high temperature and high pressure, and nutritious elements in the germ will very likely be destroyed under these conditions. Further, it will disadvantageously take a heavy load to purify the oil that has been extracted from a burned cotyledon part into odorless and tasteless soybean salad oil.
Soybean is food stuff that is very nutritious, and has been widely used as materials for various kinds of foods.
Up to now, a composition of phytosterols in the oil extracted from each part of the cotyledon, germ and hull, respectively, has been analyzed and reported (Kajimoto, G., et al., J. Jpn Oil Chem. Soc., 33 (8) 518 (1984)). But, Kajimoto, et al. did not disclose a total amount of sterol contained in said oil extracted from each part of soybean. Further, it did not disclose any cholesterol lowing effects of the oil extracted from soybean, either.
On the other hand, it is already known that oil that is supplemented with sterol (soybean sterol) that is obtained from deodorized distillate produced as a by-product during the production of soybean “tempura oil” (Japanese deep frying oil) may lower the cholesterol level in a body (Shibuya, et al., Journal of Kagawa Nutrition University 14, 173 (1983)).
The purposes of the present invention is therefore to improve a processing capacity in a crushing step, to reduce loss of the germ due to its attachment to the soybean (hull), to reduce an amount of the load in a flaking step and solvent-removing step, and to lower an amount of remaining oil in an extraction step when a soybean germ fraction is obtained from the soybean material. As a result, both the oil extracted from the germ and that from the cotyledon may be obtained without any loss, which may be then purified into soybean oil with a good taste.
Another purpose of the present invention is to provide oil that is prepared from the above fraction containing the soybean germ at a high concentration as a soybean material.
The present inventors have evaluated the above oil in an animal test with respect to its cholesterol lowering effects in a body, and found unexpectedly that it shows the cholesterol lowering effect in the body at a smaller amount of sterol contained therein than that described in the prior documents. Another purpose of the present invention is therefore to provide an agent containing said oil as an effective component for lowering cholesterol in the body of animals.